The present invention relates to a developing agent used in image formation performed by an electrophotographic method or electrostatic recording method, and a method for manufacturing the same.
Conventionally, toner used in image formation performed by an electrophotographic method is generally manufactured by a kneading pulverization method. Examples of the demands for the toner are a small particle diameter for improving the image quality, and improved low-temperature fixing properties for energy saving. Recently, however, these demands are more and more increasing, so it becomes difficult for the conventional kneading pulverization method to meet these requirements. As new toner manufacturing techniques which replace the kneading pulverization method, wet manufacturing methods, for example, are attracting attention. A typical method is an aggregation method described in, e.g., Jpn. Pat. Appln. KOKAI Publication Nos. 63-282749 and 5-11501. This aggregation method includes dispersing a toner component as submicron-order particles in water, aggregating the particles by, e.g., the addition of an aggregating agent or a salt and allowing the aggregated particles to grow to a particle diameter suitable as toner, and fusing the aggregated particles by heating. When this method is used, the particle diameter of toner particles obtained by the control of the state of aggregation can be decreased. It is also possible to control the shape by the control of heating during fusion.
Also, as described in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-26842, capsulated toner particles are obtained by using the particles obtained by the above aggregation method as cores, and coating the core surfaces with a resin to form shells. When this method is used, it is possible to prevent the conventional problem, i.e., the exposure of a releasant or coloring agent to the toner surface, and improve the durability of toner, carrier, and a photoreceptor.
Unfortunately, even when the aggregation method and capsulation described above are performed, no toner having low-temperature fixing properties which achieve energy saving and high speed has been obtained yet.
In addition, the capsulation technique has the problem that the durability of an image itself deteriorates if a material which easily melts is used as the core and a material which hardly melts is used as the shell.